Photosensitive polyimide resin compositions that can be developed with an alkaline aqueous solution to form a positive-type pattern have widely been used as materials for overcoat layers and interlayer insulating films of flexible printed circuits, sealing materials for use in IC chips, and the like. Polyimide resins have nitrogen atoms in their molecules and therefore have better flame retardancy than acrylic resins, epoxy resins, and other resins. Also from this point of view, the use of polyimide resins is recommended for such applications.
The above-described photosensitive polyimide resin compositions contain diazonaphthoquinone and a polyimide resin obtained through dehydration reaction of an aromatic diamine with an aromatic acid dianhydride having a phenolic hydroxyl group (Patent Document 1). Diazonaphthoquinone acts on the phenolic hydroxyl group in the polyimide resin to suppress the solubility of the polyimide resin in an alkaline aqueous solution. However, when irradiated with light, diazonaphthoquinone decomposes to form a ketene group and then reacts with water to form a carboxyl group. Therefore, the solubility in an alkaline aqueous solution is largely different between the exposed and unexposed areas in a thin film of the photosensitive polyimide resin composition. The exposed area can thereby be removed by developing the thin film with such an alkaline aqueous solution, whereby a positive-type pattern of the photosensitive polyimide resin composition can be formed.
[Patent Document 1] Japanese Patent Application Laid-Open No. Hei 11-202488.